The invention relates to a depositor for the manufacture of a food product from a pourable mass, especially a fatty mass such as chocolate. Depositors of this type have a tempered mass container for holding the pourable mass, at least one nozzle, which is in fluid connection with the interior of the mass container, and also a source of pressure to produce an excess pressure in the interior of the mass container.
In current practice the components of such depositors are made of rigid metal parts. The tempered mass container serves to hold the pourable mass. Pipes lead off from its base, each running into one of a number of chambers, which each have a moveable piston inside. Each of these chambers is then connected with a nozzle. A valve function is provided for each chamber/piston/nozzle unit.
During one suction stroke the respective valves open each of the connecting pipes between the mass container and each chamber, while the respective connecting pipes between each chamber and nozzle are blocked. The respective pistons then move within each chamber so as to increase the free chamber volume, and the mass is drawn into each chamber.
During one expulsion stroke the respective valves close off the connecting pipes between the mass container and each chamber, while the respective connecting pipes between each chamber and nozzle are opened. The respective pistons then move within each chamber so as to reduce the free chamber volume, and the mass is pumped out from each chamber to its assigned nozzle.
The mass coming out from the nozzle is then pressed or poured onto a supporting tray or into a hollow mould.
In the case of some special designs of such depositors, the valve function is coupled with the piston function. For this purpose the piston is for example formed as a basically cylindrical lifting/rotary piston, which is able to move in a linear stroke along the axis of the chamber or piston and also in a rotary motion around the axis of the chamber or piston. By a special arrangement of the inlets from the respective connecting pipes in each chamber wall and corresponding cut-outs and/or openings in the respective pistons, a complete pouring cycle (sucking in and ejecting) can be effected by a sequence of linear and rotary motions of the respective pistons first in one direction and then in the other, opposite direction.
Although it is true that in the latter case of the more compactly built depositors it was possible to reduce the number of moving parts to some extent by combining the piston and valve functions, such conventional depositors still have a large number of moving parts.
What is more, when pouring liquids of low viscosity it is often not possible to avoid some continued flow from the nozzle after the end of the ejection stroke. In most applications where chocolate mass is being poured, the pouring is carried out at such high temperatures that at least the crystalline variants of the triglycerides which melt at lower temperatures are melted, resulting in the chocolate mass as a whole being in a very fluid state, and some continued flow from the nozzles does take place.
Because as a rule only small quantities are poured per pouring cycle, the pouring process takes place almost entirely in the transient (non-stationary) mode. Apart from the continued flow referred to above, and the deviations from the dosage caused at least in part by this, the mainly transient mode of pouring also leads to structural changes in the mass. This can in turn lead to an impairment of the quality of the poured chocolate masses.
Besides this, it is practically impossible under the set conditions of manufacturing output levels (stroke frequency and dosage per stroke) to influence the variation over time of the flow resistance, which is conditioned by the flow properties (viscosity) of the chocolate mass to be poured and by the geometrical parameters.
The absolute pressure which is acting upstream from the nozzle must be sufficiently large to overcome the flow point of the chocolate mass to be poured, at the start of the pouring. This results in a rapid initial increase in pressure. As soon as the flow starts, a much lower pressure is needed to keep a constant flow going. What is more, due to the laminar shear current, with a parabolic kind of current profile, which is now flowing, there takes place a change in the flow properties (viscosity) of the chocolate mass, leading to a reduction in viscosity. Thus the shearing action has a thinning effect here. As a result, the pressure initially required to overcome the flow point of the chocolate mass is much larger than the pressure required to maintain the flow after the flow has started. Now this means that the design of the pressure sources and the robustness of many of the machine parts has to be worked out using this maximum pressure requirement as a basis.